Many older adults experience excessive difficulty perceiving speech in background noise. Why this occurs for some, but not all older individuals is a question that currently has no answer. Our long-term goal is to understand the biological bases of speech-in-noise perception in older adults and to use that knowledge to improve perception through training. Converging evidence indicates that the auditory sensory system (including cochlear mechanics and brainstem) is dynamic and can be shaped by short-term (training) and lifelong (language and music) experience. Normal verbal communication depends on the accurate transcription of sound by the nervous system, especially in noisy backgrounds. Failure of this transcription process in the aging population represents a huge social and financial cost, and considerable resources are invested in treatments that may not work. Little objective assessment exists in diagnosis and evaluation of treatment options. Further, there is emerging evidence that the auditory periphery is modulated by higher centers via the efferent system to aid listening in background noise. This contribution remains to be characterized and/or quantified in any detail in the human species. Accordingly, our objectives are to determine brainstem transcription of speech sounds in noise in older adults, how this transcription relates to measures of cochlear mechanics, and the plasticity of transcription with training. Our central hypothesis is that disruption of transcription accuracy and cochlear mechanics are factors in listening-in-noise impairments, and that disruption can be remedied by intervention. The outcome of the proposed work will reveal sensory mechanisms linked to speech perception in noise in older adults and determine plasticity of basic sensory circuitry arising from short-term training. This outcome will have a positive impact on our understanding and objective assessment of sensory function in aging adults.